HTS Coatings — machining & grinding

Metco 301NS

69% Ni, 13% Cr, 8% Fe, 3.5% Al, 6.5% BN

  • Plasma

Metco 301NS is an abradable seal coating, not a wear coating. That sentence tells you whether you're in the right chapter of the catalog.

The powder is an Oerlikon Metco mechanically-clad cermet: Ni balance, 13% Cr, 8% Fe, 3.5% Al, 6.5% hexagonal boron nitride (per DSMTS-0020). The Ni-Cr-Fe-Al alloy forms the matrix; the hBN is added to weaken that matrix and lubricate the rub interface. When a compressor or turbine blade tip incurs the shroud, the coating sacrifices itself to the blade — the blade cuts a clean groove, gas-path clearance holds tight, and the airfoil leaves undamaged. That's the whole point.

At HTS we spray this at 20-80 mils over a 3-10 mil NiCrAl bond coat for compressor and turbine shroud abradable seals, industrial gas turbine air seals, and steam turbine labyrinths. Service envelope is 650-815°C — the Ni-based band above where aluminum-silicon and polyester abradables give out. Hardness runs 45-58 HR15Y, designed low. Porosity 15-35%, also designed.

Do not spec Metco 301NS where wear resistance matters. It is engineered to lose a fight with a blade tip. Need durability under sliding contact? Point at Stellite 6 or HVOF WC-Co instead. Chasing clearance-control efficiency on a gas turbine? Send us the OEM callout and the shroud drawing.

Technical data

Hardness
Reported on the Rockwell 15Y superficial scale (the abradables scale, not HV): typically 45-58 HR15Y for flame-sprayed Metco 301NS; competing CoCrAlY-BN abradables run ~40 HR15Y. Deliberately soft — hardness is tuned DOWN so the coating, not the blade tip, sacrifices during rub incursions
Bond strength
~1,000-1,500 psi (7-10 MPa) for the abradable layer itself; a denser NiCrAl or NiAl bond coat (typically 3-10 mils) is sprayed first to anchor the abradable to the substrate. Reported 7.13 MPa for NiCrFeAlBN in multilayer aerospace studies — abradables are not load-bearing
Max service temp
~1200-1500°F (650-815°C) per Oerlikon Metco spec; oxidation susceptibility increases above 1200°F (650°C) but continuous service to 1380-1500°F (750-815°C) is documented in aerospace abradable applications
Max service temp
650°C continuous with conservative margin; 750-815°C maximum documented for aero-engine clearance-control service (Metco 301NS is specified for aerospace compressor/turbine abradables in the 760-815°C range)
As-sprayed porosity
15-35% typical; high porosity is by design — it reduces effective strength of the matrix so the blade tip cuts the coating cleanly rather than the blade wearing. Porosity plus the hBN lubricant phase together deliver abradability. Studies of porosity >50% show superior abradability but reduced erosion resistance
Typical thickness
20-80 mils (0.5-2.0 mm) typical abradable layer; patent literature cites 10-200 mils range with 20-100 mils preferred. Bond coat underneath runs 3-10 mils. Thickness is set by the design clearance-control envelope, not by wear allowance
Density
3.8-5.2 g/cc bulk density as-sprayed — materially lower than dense NiCrAl (~7.9) due to designed porosity + low-density hBN phase (hBN ≈ 2.3 g/cc)

Where it earns its keep

  • Abradable by design — the coating sacrifices to the rotating blade tip, maintaining tight gas-path clearance without damaging the airfoil. This is the single reason abradables exist and the single metric that matters
  • hBN additions reduce matrix strength and lubricate the rub interface — the blade cuts the coating cleanly rather than galling, work-hardening, or transferring material back to the tip
  • Extended temperature envelope vs. aluminum-silicon or polymer abradables (which top out at 480°C and 315°C respectively) — Metco 301NS is the Ni-based workhorse for the 650-815°C service band
  • Fuel-efficiency payback is substantial: 25 µm of HPT clearance reduction yields ~0.1% SFC improvement; fleet-wide this is tens of millions of gallons annually (per Oerlikon Metco aerospace data)
  • Qualified on major aerospace OEM specifications — GE, Pratt & Whitney, Rolls-Royce, Honeywell compressor and turbine shroud abradable callouts reference the 301NS / NiCrFeAlBN composition family
  • Powder flame-spray compatible — can be applied with affordable combustion equipment; also amenable to APS for thicker/denser layers

Where it doesn't

  • ABRADABLE BY DESIGN — NOT A WEAR COATING. This is the one-sentence rule. If the design intent is to resist wear from a moving part, Metco 301NS is the wrong answer; specify a dense NiCrAl, HVOF WC-Co, or Stellite instead
  • The matrix is deliberately weakened with hBN so the blade tip wins every rub. Do not substitute 301NS where hardness, load-bearing capacity, or abrasion resistance are design drivers
  • Oxidation susceptibility rises sharply above 650°C (1200°F); continuous duty above this band shortens seal life and alters rub behavior as the hBN phase is lost
  • Requires a separate bond coat (NiCrAl or NiAl, 3-10 mils) — Metco 301NS is not an all-in-one system; specify the bond coat in the process sheet or the abradable will spall
  • Erosion resistance is the main durability limit — dirty fuel, high particulate, or aggressive compressor inlet environments shorten clearance-control service life; porosity that enables abradability also enables erosion
  • Spray parameter discipline matters: published DOE studies show spray angle drives hardness (~56% contribution), standoff distance drives roughness (~80%), and oxygen flow drives porosity (~83%). Consistent abradability requires process control, not heroics

Typical applications

  • Gas turbine compressor shroud abradable seals (intermediate- and high-pressure compressor stages where temperature exceeds polymer-abradable limits)
  • Turbine shroud / blade-outer-air-seal (BOAS) abradable coatings in low- and intermediate-pressure turbine stages
  • Industrial gas turbine air seals where clearance control and fuel-efficiency gains (1-5%) drive coating selection
  • Steam turbine labyrinth seal strips and shroud rub surfaces in the hotter condensing and reheat stages
  • Aeroderivative gas turbine clearance-control surfaces in LM2500, CF6, PW series, and RB211/Trent derivatives
  • Turboprop and turboshaft engine compressor stage seals where NiCrAl-BN replaces lower-temperature aluminum-polyester abradables
  • Multilayer aero-engine seal coatings (NiCrFeAlBN + YSZ + NiCrAl bond coat) on Ti₂AlNb and superalloy shroud segments

Wear modes addressed

  • Blade-tip rub incursion — the designed wear mode; coating sacrifices material to the blade tip at a controlled cut rate, preserving gas-path clearance without transferring material to or heating the blade
  • Erosion by combustion-gas particulate (sand, ash, carbon) — the primary durability limit; high-porosity abradables erode faster than dense wear coatings
  • Oxidation of the Ni-Cr-Fe-Al matrix above 650°C, which embrittles the coating and alters rub behavior over time
  • Thermal cycling / spallation from the underlying bond coat or substrate under engine start-stop duty
  • Loss of hBN lubricant phase via oxidation at temperature, reducing abradability of aged coatings

Industries

  • Aerospace (commercial and military turbofan, turbojet, turboshaft engines — clearance control in compressor and turbine sections)
  • Industrial power generation (land-based gas turbines — Siemens SGT, GE Frame series, Mitsubishi heavy-duty and aeroderivative)
  • Marine propulsion (naval gas turbines, LM2500 and derivatives)
  • Oil & gas mechanical drive (Solar Turbines, GE LM series on offshore and midstream compression)
  • Power steam turbines (labyrinth seal and shroud strip applications in reheat and HP sections)

Substrates

  • Ni-base superalloy shroud segments (IN-718, IN-738, Waspaloy) in turbine-section housings
  • Fe-base and stainless steel compressor casings (410, 17-4 PH, A286) in cooler stages
  • Titanium-aluminide (Ti₂AlNb, γ-TiAl) advanced aero-engine shroud segments
  • Cast Ni-base and Co-base shroud rings for industrial gas turbine hot-path hardware
  • Requires a dense NiCrAl, NiAl, or equivalent bond coat (3-10 mils) for adhesion — never sprayed directly on bare substrate for production service

Which process, when?

Powder flame spray (combustion / oxy-fuel) is the classic Metco 301NS process — the 1978-era Metco 5P / 6P / 14E torches and their modern equivalents lay down the abradable at relatively low particle temperature, which preserves the hBN phase (hBN decomposes above ~1500°C in oxidizing plasmas). This is the OEM-preferred route for aerospace compressor and turbine shroud abradables. APS (Atmospheric Plasma Spray) is used for thicker deposits and for multilayer systems (NiCrFeAlBN over YSZ over NiCrAl bond coat) where higher through-thickness integrity is needed; parameters must be tuned to avoid excessive hBN burn-off. HVOF is not typical for abradables — the high-velocity, high-density regime that makes HVOF excellent for wear coatings is exactly wrong for an abradable, where porosity and hBN survival are the design targets. For an industrial shop: flame spray for standard compressor/turbine shroud repair and new-build, APS for multilayer engineered seals, and never HVOF for this family.

Sources

Data points on this page draw on the following published references. Nothing here replaces a material-specific review by our process engineers — but it's the working starting point.

Material data on this page is provided as a general reference and can vary by lot, substrate, and application. Contact HTS to confirm the right material and specification for your specific part.

Thinking about Metco 301NS for a part?

Send us the spec or a photo. We'll tell you whether this fits, or point you at a better material for the job.

Ask about this material